Thermoplastic polymers have many desirable properties that make them useful in injection molding applications. Some of these desirable properties include strength, toughness, heat resistance, and resistance to chemicals.
One problem with polyesters in injection molding applications is that it is sometimes difficult to fill large molds requiring long flow lengths or very thin parts because of the high melt viscosity of the polymer. A solution to this problem is to raise the temperature of the polymer melt, thus lowering its viscosity. This solution is often not satisfactory for polyester polymers since polyesters tend to degrade, or lose molecular weight, at elevated processing temperatures.
Also, there are well known additives which reduce the melt viscosity of polyesters. However, these additives usually make the resulting molded material less rigid, less heat resistant, and/or function only by breaking down the molecular weight of the polyester.
In U.S. Pat. No. 3,728,212, issued on Apr. 17, 1973, hot melt adhesive compositions which consist of a blend of poly(tetramethylene terephthalate) with polystyrene or a polystyrene copolymer are disclosed. No other uses for these blends are disclosed.
Also, U.S. Pat. No. 3,290,411 describes methods of making blends principally with styrene polymers and conversion of the blends into fibers.
However, the prior art does not show the desirability of using blends of a polyester and a styrene methyl methacrylate copolymer in injection molding applications.